Ethylene and propylene are light olefin hydrocarbons with two or three atoms per molecule, respectively, and are important chemicals for use in the production of other useful materials, such as polyethylene and polypropylene. Polyethylene and polypropylene are two of the most common plastics found in use today and have a wide variety of uses for both as a material fabrication and as a material for packaging. Other uses for ethylene and propylene include the production of vinyl chloride, ethylene oxide, ethylbenzene and alcohol. Steam cracking or pyrolysis of hydrocarbons produces essentially all of the ethylene and propylene. Hydrocarbons used as feedstock for light olefin production include natural gas, petroleum liquids, and carbonaceous materials including coal, recycled plastics or any organic material.
A light olefin plant is a very complex combination of reaction and gas recovery systems. The feedstock is charged to a cracking zone in the presence of steam at effective thermal conditions to produce a pyrolysis reactor effluent gas mixture. The pyrolysis reactor effluent gas mixture is stabilized and separated into purified components through a sequence of cryogenic and conventional fractionation steps. A typical light olefin plant includes an ethylene separation section containing both cryogenic and conventional fractionation steps to recover an ethylene product with a purity exceeding 99.5% ethylene. Propylene and heavier hydrocarbons are separated from the ethylene and recovered in a separate section, or separate fractionation column.
Simplification of the process can save energy, and capital cost, while increasing the overall yields of product.